1. Field of the Invention
The present invention relates to a printing apparatus and a method for conveying a sheet wherein a printed sheet is discharged after being aligned with a predetermined sheet discharging position.
2. Description of the Related Art
Printing apparatuses such as printers include a sheet discharging mechanism for discharging a sheet completely printed by a printing section after aligning the sheet with a predetermined sheet discharging position outside the apparatus. The sheet discharging mechanism in such a printing apparatus is configured such that a sheet discharging roller that is rotated by a driving source is compressed against a sheet and then rotated to exert a conveying force on the sheet, which is thus discharged to the exterior of the apparatus and stacked in a stacker.
In a series of operations from feeding of a sheet through printing by a printer or the like to sheet discharging, the volume of noise from the printing apparatus tends to increase consistently with the speed at which the sheet is conveyed. Thus, to reduce the volume of the noise from the printing apparatus, the sheet conveying speed needs to be decreased. Hence, some printing apparatuses are configured to provide a silent setting so that when a user selects the silent setting, the sheet conveying speed is reduced to lower the volume of the noise from the printing apparatus.
However, when a sheet is discharged from the sheet discharging roller and the sheet conveying speed is reduced, the force of the sheet discharging roller pushing the sheet out into the stacker with already discharged sheets stacked is decreased. Thus, even when the sheet discharging roller pushes the sheet out, the frictional force between the discharged sheet and the stacker or the sheets stacked in the stacker prevents the discharged sheet from reaching a regular position where the sheet is to be stacked. Consequently, the discharged paper may fail to be properly aligned with the stacker. Hence, a printing apparatus has been proposed which properly aligns the sheet discharged from the sheet discharging roller with the stacker by setting the sheet conveying speed to a given value or larger.
For example, in connection with a print medium conveying and discharging apparatus disclosed in Japanese Patent Laid-Open No. 2008-273636, a configuration of a sheet discharging mechanism has been proposed which changes a conveying speed between a conveying speed at which a sheet is conveyed by both a conveying roller and the sheet discharging roller and a conveying speed at which the sheet is conveyed only by the conveying roller. That is, when the sheet is conveyed by both the conveying roller and the sheet discharging roller, the conveying speed of the sheet discharging roller is set equal to the normal conveying speed of the conveying roller. Furthermore, when the sheet is conveyed only by the sheet discharging roller, the conveying speed of the sheet by discharging roller is set to a relatively high conveying speed suitable for alignment of a discharged sheet.
However, the print medium conveying and discharging apparatus in Japanese Patent Laid-Open No. 2008-273636 uses different driving sources for the sheet discharging roller and the conveying roller. Thus, the sheet discharging roller and the conveying roller are controlled so as to be rotated at different rotation speeds. In general, in view of the manufacturing cost of the printing apparatus, if the printing apparatus includes a plurality of roller pairs such as the conveying roller and the sheet discharging roller, a common driving source is preferably used to drive these roller pairs. Decreasing the number of driving sources in the printing apparatus in this manner enables an eventual reduction in the manufacturing cost of the printing apparatus. Hence, if the different driving sources are used for the sheet discharging roller and the conveying roller as in the printing apparatus disclosed in Japanese Patent Laid-Open No. 2008-273636, the manufacturing cost of the printing apparatus increases.
Furthermore, in the print medium conveying and discharging apparatus disclosed in Japanese Patent Laid-Open No. 2008-273636, the conveying speed at which a sheet is conveyed is set so as to be relatively high in a section where sheet is conveyed only by the sheet discharging roller and to be relatively low in a section where the sheet is conveyed by both the conveying roller and the sheet discharging roller. Thus, in the state where the sheet is conveyed only by the sheet discharging roller, the sheet is simply discharged at the higher speed. With the conveying speed thus set, even if an attempt is made to reduce the section where the sheet is conveyed at the relatively high conveying speed in order to inhibit possible noise, the setting of the length of the section is limited by the configuration of the apparatus. In particular, many printing apparatuses in which a printing area is provided between the conveying roller and the sheet discharging roller is adopted. In this case, a space for the printing area needs to be provided in the printing apparatus between the conveying roller and the sheet discharging roller. This limits the reduction in the distance between the conveying roller and the sheet discharging roller which is intended to decrease the section where the sheet is conveyed at the relatively high conveying speed. Consequently, even though a relatively long distance remains between the trailing end of a sheet and the sheet discharging position, the sheet is conveyed over a long section at the high conveying speed. Therefore, the state of noise at the high conveying speed may be continued for a long time.